Rubber molded article vulcanizing mold, and method for cleaning the same

ABSTRACT

Semi-circular cover members  17  and  17  having a spring function for opening and closing the openings of pores  15 S are provided on the cavity inner wall side of a porous air vent  15  in order to close the openings of the above pores  15 S while a small space remains between the above cover members  17  and  17  and the openings of the pores  15 S of the porous air vent during vulcanization, whereby the occurrence of the occlusion of the above pores  15 S is reduced and stains adhered to the cavity inner wall side of the mold  10  are removed by physical means such as a blast treatment while the above cover members  17  and  17  are closed at the time of cleaning to remove the stains of the above mold  10 . Further, the above openings are opened as required to allow a cleaning liquid  24  go into the above pores  15 S to clean the above mold  10  and remove stains in the pores  15 S.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vulcanizing mold for vulcanizing andmolding a rubber molded article such as a tire and to a cleaning methodfor the same.

2. Description of the Prior Art

To form a tire, a vulcanizing mold (to be referred to as “mold”hereinafter) is used in which pressure is applied to the inside of themolded green tire to pressure contact the outer surface of the abovegreen tire to the inner wall of the heated mold in order to vulcanizethe crude rubber by heat and pressure. Exhaust passages such asmicro-vents, slits, vent holes or cross vents are formed in this mold toremove air contained between the outer surface of the tire and the moldand gas generated from the green tire. However, when the abovemicro-vents, slits, vent holes or cross vents are used, a rubbermaterial enters the holes of the vents during molding and a large numberof projections called “spew” are formed on the surface of the vulcanizedtire, thereby impairing the appearance of the tire. Therefore, trimmingis indispensable. Even when trimming is carried out, the height oftrimming may vary or part of the tire may be untrimmed, which is notpreferred from the viewpoint of the appearance of the tire. In addition,a trimming apparatus is required, thereby boosting cost. Since theocclusion of vent holes caused by the slivering of spew occurs in themold, the spew must be removed by using a tool such as a drill. However,as there are hundreds of vent holes in the mold, the work of removingthe spew takes a lot of time and labor. In the case of cross vents, thespew cannot be removed by using a tool or the like.

A film-like projection called “lip” is formed in the case of slits,which is not preferred from the viewpoint of the appearance of the tire.When a large lip crossing the main groove of the tire is formed, it maydam the main groove having a drainage function to prevent drainage,thereby causing a problem with safety driving, such as triggering ofhydro-planing while driving on a wet road.

To cope with the above problem, a mold having porous air vents, eachcomprising a porous member having a large number of pores fortransmitting only gas formed in a substrate such as a metal substrate ora porous member made from a porous material having a large number ofpores such as a sintered metal, has been developed as a mold which doesnot require the above trimming step.

FIGS. 9(A) to (C) show an example of a vulcanizing mold 10P for rubbermolded articles having porous members of the prior art. This vulcanizingmold 10P for rubber molded articles is made by putting together aplurality of segments 11 into a substantially cylindrical form, and anopening 12 into which a rubber material (bladder) for supplying a greentire to be vulcanized, heat and pressure is inserted is formed in thecore portion of the above mold 10P. Each of the above segments 11consists of an outer case 51 made from a steel material and a pluralityof aluminum pieces 52 secured to the inner wall of the outer case 51 byunshown bolts. The surfaces (portions exposed to the inner wall of themold 10P) of the above pieces 52 are tire forming surfaces, that is,portions to which the rubber of the green tire to be vulcanized iscontacted.

A plurality of holes 52S which communicate with exhaust holes to bedescribed hereinafter formed in the outer case 51 are formed in each ofthe above pieces 52. A plurality of vent pieces (to be referred to as“porous air vent” hereinafter) having a large number of straight pores53S with a diameter of 10 to 40 μm and communicating with the exhaustholes 51S of the outer case 51 are fitted in the respective holes 52S asshown in FIGS. 10(A) and 10(B). In FIG. 10(B), an upper side (piece 52side) of the figure is a rubber side and a lower side (outer case 51side) of the figure is a mold side. Thereby, air between the mold 10Pand the outer surface of the tire and gas generated from the green tireduring vulcanization are absorbed from the above pores 53S which areexhaust passages by unshown exhaust means such as a vacuum pumpconnected to the above exhaust holes 51S and discharged to the outsideof the mold 10P from the exhaust holes 51S of the outer case 51 througha gap 54 between the pieces 52 and the outer case 51.

However, in the porous air vent 53 of the prior art, as shown in FIG.11, since the diameters of the above pores 53S are fixed from the cavityside to the opposite side (outer case 51 side), when the occlusion ofthe pores 53S by plug materials p such as oil, chemicals and metal fumesdischarged from the green tire during vulcanization and fine particlesof a polymer and carbon occurs on the cavity side, it is difficult todischarge the above plug materials p to the exhaust side (outside of themold 10).

When the above plug materials p adhere to the cavity side of each pore53S like tar, the passage of the air vent is narrowed and the plugmaterials adhere to the pores 53S more easily and form a bridge toocclude the pores 53S, thereby greatly reducing exhaust efficiency andcausing a tire failure in an early stage. Therefore, the above mold 10Pmust be cleaned frequently and the operation efficiency of the mold lopis low. Once the porous member is plugged, it is extremely difficult toremove the plug materials with a drill or the like. Particularly whenthe porous member is a sintered metal, as each opening constituting aventilation passage is not straight, a special cleaning method must beused and it is difficult to clean the mold. When a sintered metal isused as the porous member, the meshed patch of each vent is formed onthe surface of a tire, impairing the appearance of the tire.

When vulcanization is repeated, plug materials such as a rubber materialand a polymer produced by the slivering of spew and fine particles ofcarbon adhered during vulcanization are firmly adhered to the surface ofthe mold, thereby staining the surface of the mold. To remove thesestains on the surface of the mold, the following methods have beenemployed.

-   (1) physical methods for blasting a shot of plastic beads or glass    beads, or dry ice, affixing cleaning rubber, or applying a laser    beam or a jet of high-pressure water (so-called peeling; peeling of    adhered products)-   (2) physico-chemical methods making use of plasma, ultra-criticality    to pseudo-criticality, and electrolysis-   (3) chemical methods for immersing a mold in an amine-based cleaning    liquid (+), oxygen-based cleaning liquid or sodium bicarbonate-based    cleaning liquid to expand stains and removing them by high-pressure    water.

However, in the methods (1), only stains on the surface of the mold canbe removed but stains in the exhaust passages cannot be removed and thesurface of the mold may be damaged. In the methods (2), the electricerosion/melting or deformation/modification of the surface of the moldeasily occurs.

In the methods (3), it takes time because the mold is cleaned only witha cleaning liquid, the cleaning liquid is apt to deteriorate, andchemical treatment equipment is needed. Therefore, the methods haveeconomical and spatial problems.

It is an object of the present invention which has been made in view ofthe above problems of the prior art to provide a vulcanizing mold forrubber molded articles which suppresses the occurrence of the occlusionof exhaust passages with plug materials and makes cleaning easy as wellas a method of cleaning the mold.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided Avulcanizing mold for rubber molded articles having air vents, eachhaving exhaust passages opened to a cavity inner wall side at one endand communicating with the exhaust holes of the mold at the other end,wherein a movable valve for opening and closing the openings of theexhaust passages and forming a small gap with the openings of theexhaust passages when it is closed is provided on the cavity inner wallside of each of the air vents and is closed during vulcanization torestrict the entry of plug materials into the exhaust passages in orderto reduce the occlusion of the exhaust passages and the prevent theproduction of spew.

According to a second aspect of the invention, there is provided avulcanizing mold for rubber molded articles, wherein the movable valveis composed of one or more cover members having an opening/closingmechanism.

According to a third aspect of the invention, there is provided avulcanizing mold for rubber molded articles, wherein the cover membersare a pair of semi-circular plates.

According to a fourth aspect of the invention, there is provided avulcanizing mold for rubber molded articles, wherein the movable valveis a plate-like cover member having a spring function to be urged towardan open direction. Accordingly, the cover member is attracted toward theair vent by suction by means of exhaust means of the mold duringvulcanization to close the exhaust passages and restrict the entry ofplug materials into the above exhaust passages. Since the cover memberis opened by the above spring mechanism at the time of cleaning, theinsides of the exhaust passages can be easily cleaned.

According to a fifth aspect of the invention, there is provided avulcanizing mold for rubber molded articles, wherein a stepped portionis formed by sputtering or etching the exhaust passage side of the covermember, and a gap between the cover member and the openings of theexhaust passages is maintained by this stepped portion.

According to a sixth aspect of the invention, there is provided avulcanizing mold for rubber molded articles, wherein the air vents areporous air vents, each having a porous member with a large number ofpores which transmit only gas.

According to a seventh aspect of the invention, there is provided amethod of cleaning a vulcanizing mold for rubber molded articles havingair vents, each having exhaust passages opened to a cavity inner wallside at one end and communicating with the exhaust holes of the mold atthe other end, the method comprising removing stains adhered to thecavity inner wall side while a movable valve for opening and closing theopenings of the exhaust passages and forming a small gap with theopenings when it is closed is closed. That is, since the above movablevalve is closed during vulcanization to restrict the entry of plugmaterials into the above exhaust passages, the rear side of the abovemovable valve and the exhaust passages are rarely stained. Therefore,the stains of the mold can be completely removed by separating stains onthe cavity inner wall side including the front side of the movable valvewhile the movable valve is closed.

According to an eighth aspect of the invention, there is provided amethod of cleaning a vulcanizing mold for rubber molded articles havingair vents, each having exhaust passages opened to a cavity inner wallside at one end and communicating with the exhaust holes of the mold atthe other end, the method comprising allowing a cleaning liquid go intothe exhaust passages by opening the openings of the exhaust passages bymeans of a movable valve for opening and closing the openings andforming a small gap with the openings when it is closed to clean themold.

According to a ninth aspect of the invention, there is provided a methodof cleaning a vulcanizing mold for rubber molded articles, wherein thepressure on the cavity inner wall side is reduced after cleaning and thestains are discharged to the cavity inner wall side.

According to a tenth aspect of the invention, there is provided a methodof cleaning a vulcanizing mold for rubber molded articles, whereincleaning is ultrasonic cleaning.

According to an eleventh aspect of the invention, there is provided amethod of cleaning a vulcanizing mold for rubber molded articles,wherein ultrasonic cleaning is carried out while ultrasonic wavegenerating means and the mold are moved relative to each other.

According to a third aspect of the invention, there is provided a methodof cleaning a vulcanizing mold for rubber molded articles according toany one of claims 8 to 11, wherein cleaning is carried out by settingthe temperature of the cleaning liquid to 35 to 80° C.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an example of a vulcanizing mold for rubbermolded articles according to the best embodiment of the presentinvention;

FIG. 2 is a diagram showing the constitution of segments of thevulcanizing mold for rubber molded articles according to the bestembodiment of the present invention;

FIG. 3 is a partial sectional view showing the constitution of segmentsof the vulcanizing mold for rubber molded articles according to the bestembodiment of the present invention;

FIGS. 4(A) and 4(B) are diagrams for explaining the function of movablevalves according to the best embodiment of the present invention;

FIGS. 5(A) and 5(B) are diagrams showing a method of cleaning thevulcanizing mold for rubber molded articles according to the bestembodiment of the present invention;

FIGS. 6(A) and 6(B) are diagrams showing the method of cleaning thevulcanizing mold for rubber molded articles according to the bestembodiment of the present invention;

FIG. 7 is a diagram showing a post-treatment after ultrasonic cleaning;

FIGS. 8(A) to 8(D) are diagrams of other examples of the vulcanizingmold for rubber molded articles of the present invention;

FIGS. 9(A) to 9(C) are diagrams showing the constitution of avulcanizing mold for rubber molded articles having porous air vents ofthe prior art;

FIGS. 10(A) and 10(B) are diagrams showing the constitution of a porousair vent of the prior art; and

FIG. 11 is a diagram showing the state of the occlusion of the porousair vent of the prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The best embodiment of the present invention will be describedhereinbelow with reference to the accompanying drawings.

FIG. 1 is a diagram showing the basic constitution of a vulcanizing mold10 for rubber molded articles according to the best embodiment of thepresent invention. The vulcanizing mold 10 for rubber molded articles ofthe present invention is constructed by combining a plurality ofsegments 11 into a substantially cylindrical form and has an opening 12into which a rubber material (bladder) is inserted. As shown in FIG. 2,each of the above segments 11 consists of an outer case 13 made from asteel material and a plurality of pieces 14 made from aluminum andsecured to the inner wall of the outer case 14 by bolts. The surfaces(portions exposed to the inner wall of the mold 10) of the above pieces14 are tire forming surfaces, that is, portions to which crude tirerubber to be vulcanized is contacted.

A plurality of holes 14S communicating with exhaust holes which will bedescribed hereinafter and are formed in the outer case 13 are formed ineach of the above pieces 14, and a porous air vent 15 having a largenumber of pores 15S is fitted in each of the holes 14S. As shown in FIG.3, the above pores 15S communicate with the exhaust holes 13S of theouter case 13 through a gap 16 between the pieces 14 and the outer case13. The exhaust holes 13S are connected to a filter 20 for removingrubber powders and the like and to a vacuum pump (VP) 21 for absorbingair in the mold 10 and a gas generated during vulcanization.

In this embodiment, as shown in FIG. 2 and FIG. 3, semi-circular covermembers 17 and 17 having a spring function for opening and closing theopenings of the above pores 15S are provided on the cavity inner wallside (tire forming side) of the above porous air vent 15. The covermembers 17 and 17 can be constructed by attaching leaf springs having aspring function which are urged to be opened toward the tire formingside to the periphery of the porous air vent 15. As shown in FIG. 4(A),the strength of the above springs is preferably adjusted such that thefree ends 17 c of the cover members 17 and 17 in an open state projecttoward the tire forming side by a distance H of 1 mm or less.

Since the above pores 15S communicate with the exhaust pores 13S throughthe gap 16 as described above, the vacuum pump (VP) 21 is activated atthe time of vulcanization so that the above cover members 17 and 17 areabsorbed toward the porous air vent 15 side as shown in FIG. 4(B) toclose the openings of the pores 15S, or the above cover members 17 and17 are closed by the pressure of the bladder. If rubber waste isgenerated on the above cover members 17 and 17, it will be dischargedtogether with part of the tire as projecting rubber of the tire aftervulcanization and therefore will not be accumulated in the pores 15S.

When the cover members 17 and 17 are closed, a very small gap G havingan interval of 0.5 μm or less is formed between the above cover members17 and 17 and the openings of the pores 15S. The above gap G may beformed by depositing a thin film layer as a spacer on part of the rearsurfaces (porous air vent 15 side) of the above cover members 17 and 17by sputtering or by removing part of the peripheral portions of the rearsurfaces of the cover members 17 and 17 to form a spacer by etching orthe like. Alternatively, the cover member 17 may be made circular andformed by sputtering or etching.

Therefore, at the time of vulcanization, as shown in FIG. 4(B), a plugmaterial p larger than the above gap G does not reach the openings ofthe above pores 15S and only a plug material smaller than the gap G istaken into one of the pores 15S. The above small plug material easilypasses through the pore 15S of the porous air vent 15 and is dischargedto the outside of the mold 10 from the exhaust hole 13S of the outercase 13 through the gap 16. Therefore, the occurrence of the occlusionof the above pores 15S can be greatly reduced and exhaust efficiency canbe improved.

Since the porous air vent 15 of this embodiment restricts the exhaustroute to the pores 15S by means of the above gap G, the production ofspew is rare and therefore a trimming step is not required.

In the mold 10 of this embodiment, if the cover members 17 and 17 aredamaged or lost, only the cover members 17 and 17 may be exchanged.Thus, repair is easy. When the occlusion of the pores 15S is caused bythe damage of the cover members 17 and 17, the porous air vent 15 isdesirably exchanged.

A description is subsequently given of the method of cleaning the mold10 for rubber molded articles having the above constitution.

First, as shown in FIG. 5(A) and 5(B), the unshown vacuum pump (VP) isactivated to absorb the above cover members 17 and 17 toward the porousair vent 15 side to close the openings of the pores 15S as the time ofvulcanization. Then, a blast treatment for blasting a resin material Rhaving relatively low hardness from a blast device 22 to the inner wall(tire forming side) of the mold 10 through a spray nozzle 22N is carriedout to remove stains adhered to the surface of the mold 10. Thereby,almost 95% of all the stains can be removed.

Subsequently, as shown in FIGS. 6(A) and 6(B), the above mold 10 isimmersed in a cleaning liquid 24 maintained at 35 to 80° C. in acleaning tank 23 to clean the above mold 10 while ultrasonic waves aregenerated in the above cleaning liquid 24 by ultrasonic wave generatingmeans 25. At this point, as the cover members 17 and 17 are openedtoward the tire forming side (inner wall side of the mold 2) by theirspring function to open the openings of the pores 15S, the cleaningliquid 24 can go into the pores 15S easily. Since the above covermembers 17 and 17 are closed to restrict the entry of the plug materialsinto the pores 15S during vulcanization as described above, the rearsides of the above cover members 17 and 17 and the insides of the pores15S are rarely stained. Therefore, stains of the mold 10 can be easilyremoved by above ultrasonic cleaning.

When ultrasonic waves are applied from various directions of the mold 10by moving the above ultrasonic wave generating means 25 in the cleaningliquid 24 horizontally or vertically, or turning the mold 10 in thecleaning liquid 24, stains in the pores 15 s can be completely removed.The ultrasonic wave generating means 25 can be preferably movedvertically or turned in the opening 12 of the mold 10.

The above cleaning liquid 24 preferably contains aluminum which is thematerial of the mold 10 or a component which can prevent corrosion suchas iron or SUS.

After cleaning, the ultrasonic wave generating means 25 is lifted tocollect the cleaning liquid 24, the opening 12 of the mold 10 is coveredwith covers 26 and 26 as shown in FIG. 7, the inside of the mold 10 isdepressurized by using a vacuum pump 27 to discharge the stains of themold 10 to the inner wall side of the mold, and the mold 10 is rinsed inwater containing a rust preventive and dried. The mold 10 is dried byheating at 70 to 130° C. and further depressurized by the vacuum pump 27to completely drain water, which is preferred as a pre-treatment beforevulcanization.

Thereby all the stains of the mold 10 are removed.

Thus, in this embodiment, the semi-circular cover members 17 and 17having a spring function for opening and closing the openings of thepores 15S are attached to the cavity inner wall side of the porous airvent 15, and the openings of the pores 15S are closed while a very smallgap remains between the above cover members 17 and 17 and the openingsof the pores 15S of the porous air vent during vulcanization. Therefore,the occurrence of the occlusion of the above pores 15S can be greatlyreduced, exhaust efficiency can be improved, and a tire which rarelysees the production of spew or lip can be molded.

In this embodiment, since vulcanization is carried out while theopenings of the above pores 15S are closed by the above cover members 17and 17, the pores 15S are rarely stained, whereby at the time ofcleaning, stains adhered to the cavity inner wall side of the mold 10are removed by physical means such as a blast treatment while the abovecover members 17 and 17 are closed, thereby making it possible tocompletely remove the stains of the above mold 10. Further, when theabove openings are opened to allow the cleaning liquid 24 go into theabove pores 15S so as to clean the above mold 10, stains in the pores15S can be removed completely and easily.

In the above best embodiment, two semi-circular cover members 17 and 17are used. The present invention is not limited to this embodiment andthe cover members 17 may cover the openings of the pores 15S duringvulcanization. Therefore, the number and shape of the cover members maybe suitably determined according to the size and shape of the mold 10 orthe porous air vent 15.

The porous air vent 15 has been described in the above embodiment. Ahomogenous air vent 31 having a stepped exhaust pore 31S as shown inFIG. 8(A), a homogeneous air vent 32 having a tapered exhaust pore 32Sas shown in FIG. 8(B), and a homogeneous air vent 33 having an exhaustpore 33S with a thread as shown in FIG. 8(C) may also be used. In thesecases, a circular cover member 30 manufactured by sputtering or etchingmay be used as the cover member. Further, when the circular cover member30 manufactured by sputtering or etching is used, a homogeneous air vent34 having a straight exhaust pore 34S as shown in FIG. 8(D) may be used.

INDUSTRIAL FEASIBILITY

As having been described above, according to the present invention, in avulcanizing mold for rubber molded articles having air vents, eachhaving exhaust passages opened to a cavity inner wall side at one endand communicating with the exhaust holes of the mold at the other end, amovable valve for opening and closing the openings of the exhaustpassages and forming a small gap with the openings of the above exhaustpassages when it is closed is provided on the cavity inner wall side ofeach of the above air vents, and the above movable valve is closedduring vulcanization to restrict the entry of plug materials into theabove pores. Therefore, the occlusion of the air vents can be reduced,exhaust efficiency can be improved, and a tire which rarely sees theproduction of spew or lip can be molded.

Since the above movable valve is closed during vulcanization and theentry of plug materials into the above exhaust passages is restricted,the rear side of the above movable valve and the exhaust passages arerarely stained, and the stains of the mold can be completely removedsimply by separating stains adhered to the cavity inner wall side whilethe movable valve is closed.

Further, when the above mold is cleaned by opening the above openings toallow the cleaning liquid go into the above exhaust passages, not onlystains on the surface of the mold but also stains in the exhaustpassages can be completely removed.

1. A vulcanizing mold for rubber molded articles having air vents, eachhaving exhaust passages opened to a cavity inner wall side at one endand communicating with the exhaust holes of the mold at the other end,wherein a movable valve for opening and closing the openings of theexhaust passages and forming a small gap with the openings of theexhaust passages when the movable valve is closed which is provided onthe cavity inner wall side of each air vent.
 2. The vulcanizing mold forrubber molded articles according to claim 1, wherein the movable valveis composed of one or more cover members having an opening/closingmechanism.
 3. The vulcanizing mold for rubber molded articles accordingto claim 2, wherein the cover members are a pair of semi-circularplates.
 4. The vulcanizing mold for rubber molded articles according toany one of claims 1 to 3, wherein the movable valve is a plate covermember having a spring function to be urged toward an open direction. 5.The vulcanizing mold for rubber molded articles according to any one ofclaims 2 to 3, wherein a stepped portion is formed by sputtering oretching the exhaust passage side of the cover member, and a gap betweenthe cover member and the openings of the exhaust passages is maintainedby the stepped portion.
 6. The vulcanizing mold for rubber moldedarticles according to any one of claims 1 to 3, wherein the air ventsare porous air vents, each having a porous member with a large number ofpores which transmit only gas.
 7. The vulcanizing mold for rubber moldedarticles according to claim 1, wherein the small gap permits release ofgas or small plug materials that are discharged through thevulcanization operation.